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Cosmological redshift  z  grows as the Universe expands and is conventionally viewed as a third form of redshift, beyond the more traditional Doppler and gravitational effects seen in other applications of general relativity. In this paper, we examine the origin of redshift in the Friedmann–Robertson–Walker (FRW) metrics with constant space–time curvature, and show that – at least for the static space–times – the interpretation of  z  as due to the ‘stretching’ of space is coordinate dependent. Namely, we prove that redshift may also be calculated solely from the effects of kinematics and gravitational acceleration. This suggests that its dependence on the expansion factor is simply a manifestation of the high degree of symmetry in FRW, and ought not be viewed as evidence in support of the idea that space itself is expanding.

Cosmological redshift in Friedmann–Robertson–Walker metrics with constant space–time curvature